1. Field of the Invention
The present invention relates to a toner transport roller having a sealing member, for preventing leak of toner, which contacts a peripheral surface of a rubber roller slidably. More particularly, present invention relates to the toner transport roller capable of restraining wear of a sealing portion thereof by efficiently dissipating heat generated by friction between the sealing member and the rubber roller when the sealing member slidably contacts the rubber roller and capable of preventing leak of toner. The toner transport roller is used preferably as a developing roller.
2. Description of the Related Art
In recent years, in the printing technique using the electrophotographic method, a high-speed printing operation, formation of a high-quality image, formation of a color image, and miniaturization of image-forming apparatuses have been progressively made and become widespread. Toner holds the key to these improvements. To satisfy the above-described demands, it is necessary to form finely divided toner particles, make the diameters of the toner particles uniform, and make the toner particles spherical. Regarding the technique of forming the finely divided toner particles, toner having a diameter not more than 10 μm and toner not more than 5 μm have been developed recently. Regarding the technique of making the toner spherical, toner having not less than 99% in its deviation from a spherical form has been developed. To form the high-quality image, polymerized toner has come to be widely used instead of pulverized toner conventionally used. The polymerized toner allows the reproduction of dots to be excellent in obtaining printed matters from digital information and hence a high-quality printed matter to be obtained.
In correspondence to the improvement in the technique of forming finely divided toner particles, making the diameters of the toner particles uniform, making the toner particles spherical, and the transition from the pulverized toner conventionally used to the polymerized toner, members constituting the image-forming apparatus adopting the electrophotographic method are demanded to have high-performance function and durability allowing the function of each member to be maintained to the last of the use life of the image-forming apparatus and the like.
To comply with such a demand, by mixing the loss tangent-adjusting filler with the ionic-conductive rubber uniform in its electrical characteristic, the present inventors have developed the conductive rubber roller (disclosed in Japanese Patent Application Laid-Open No.2004-170845 (patent document 1)) uniform in its electrical characteristic, superior in its property of electrically charging toner and the like, and capable of keeping the property of electrically charging the toner and the like.
The above-described conductive rubber roller is capable of keeping the charged amount of toner at a high level and is thus improving the transportability of the toner. But there is room for improvement for the durability of the conductive rubber roller.
To improve the durability of the rubber roller and allow it to display a high function reliably for a long time, it is important for the following rollers (described below) to faithfully transport toner which is very small and has a good shape to a subsequent member of an image-forming apparatus. The above-described rollers include a developing roller for supplying a certain amount of toner to a subsequent part of the image-forming apparatus, an electrophotographic photoreceptor, a transfer roller, and a cleaning roller for collecting toner which has not been transferred and remained on the transfer roller. It is also important for each member of the image-forming apparatus not to leak the toner to the inside thereof.
More specifically, the annular sealing member is slidably fitted on both axial ends of the rubber roller which transports the toner. Finely divided toner is liable to penetrate into a boundary partitioning the transport part and the non-transport part from each other, namely, the sliding-contact portion between the peripheral surface of the rubber roller and the inner peripheral surface of the sealing member. The spherical toner penetrates into the sliding-contact portion to a higher extent owing to its configuration. The penetration of the toner into the sliding-contact portion causes the rubber roller and the sealing member to contact each other through the toner. As a result, a high pressure is applied to the sliding-contact portion to generate heat violently. The generated heat causes the rubber roller and the sealing member to be worn to a high extent and the toner to leak in its turn. In the case of the polymerized toner, thermoplastic resin composing the toner melts. As a result, toner particles become large and edged and are welded to each other to form angular large particles. Thereby the rubber roller and the sealing member are destroyed acceleratedly. The peripheral surface of the rubber roller and the inner peripheral surface of the sealing member slide in contact with each other to generate heat. Thus even though the toner does not penetrate into the sliding-contact portion, the rubber roller and the sealing member are worn to generate a gap therebetween. Thereby the toner is liable to penetrate thereinto. The above-described problem will occur with time owing to the penetration of the toner thereinto.
The following inventions have been made to solve the above-described problem which occurs owing to the heat generated by the sliding contact between the rubber roller and the sealing member.
Disclosed in Japanese Patent Application Laid-Open No. 2002-91158 (patent document 2) is the one-component developing roller having the space formed inside the developing roller and the heat dissipation portion, formed at both ends of the developing roller, which allows communication between the outside air and the space.
In the description made in the specification, the above-described construction dissipates the heat generated at the portion of contact between the developing roller and the toner restriction member to the outside, thereby preventing the rise of temperature and aggregation and adherence of toner particles.
Disclosed in Japanese Patent Application Laid-Open No. 2002-278386 (patent document 3) is the image-forming apparatus having the developer agitation/transport member, disposed near the developing roller, which is composed of the highly thermal heat-conductive member such as a heat pipe. The image-forming apparatus further includes the heat dissipation (heat exchange) fin provided at the end of the developer agitation/transport member. According to the description made in the specification, this construction suppresses the influence of heat given by portions other than the image-forming portion and improves the cooling effect.
However, this construction causes the image-forming apparatus to be large and further the cooling speed to be differentiated in dependence on a flow speed of air and positions of members. Thus there is a possibility that some portions have a low toner transportability.
Patent document 1: Japanese Patent Application Laid-Open No. 2004-170845
Patent document 2: Japanese Patent Application Laid-Open No. 2002-91158
Patent document 3: Japanese Patent Application Laid-Open No. 2002-278386